Adding just that little bit of space below the Dad's elbow, the way The_Traveler did, makes the image feel more peaceful, more in-balance, more "tranquil" if you will. Having a person's elbow or hand or face, whatever, right AT the edge of the frame, causes a visual tension. Sometimes that tension can work, and other times, the tension detracts. Adding that additional bit of space (enlarging the 'canvas' as it is called in PS) is a smart move by The_Traveler.
As to the baby's face being brighter than the Dad's face...that's a 50/50 call I think...toning the face of the baby down increases the baby/Dad harmony, makes them seem connected (more identically-lighted I guess)....leaving the baby's face brighter also works too.
I would consider this image to be a likely candidate for a square crop!